The present invention generally relates to fiber optic communications and, more particularly, to a 2-dimensional, mechanical, fiber optical cross-connect switch.
Fiber optical cross-connect switches find wide application in communications, for example, in the telecommunications industry, where fiber optical switches may be used for metro and long haul services using dense wavelength division multiplexing (DWDM). DWDM is a technology that uses multiple lasers and transmits several wavelengths of light simultaneously over a single optical fiber. Each signal travels within its unique color band, which is modulated by the data (text, voice, video, for example). DWDM enables the existing fiber infrastructure of the telephone companies and other carriers to be dramatically increased. DWDM systems exist that can support more than 150 wavelengths, each carrying data at rates up to 10 billion bits per second (Gbps). Such systems can provide more than 1,000 Gbps of data transmission on one optical fiber.
Conventional fiber optical cross-connect switches that connect optical fiber lines are electro-optical. Such conventional switches convert photons from the input side to electrons internally in order to do the signal switching electronically and then convert back to photons on the output side. Such conventional switches may typically be used, for example, in a central office core router of a telecommunications network. By way of contrast, an all-optical fiber-optical cross-connect switch is a switching device that maintains the signal as light from input to output. Although some vendors call electro-optical switches “optical switches,” true optical switches, i.e., all-optical switches, support all transmission speeds. Unlike electronic switches, which are tied to specific data rates and protocols, all-optical switches direct the incoming data bit stream to the output port no matter what the line speed or protocol (such as internet protocol (IP), asynchronous transfer mode (ATM), or synchronous optical network (SONET)) and do not have to be upgraded for any changes to the protocol.
An optical switch is a device that switches a small and collimated beam of light in free space either to be passed through a location unaffected or to be reflected in a different direction at the location. The switching can be done mechanically by moving a mirror between two distinct and stable positions—in the path of the light, and out of the path of the light. An optical cross-connect switch may allow light to be routed between optical fibers in such a way that any optical fiber from one side of the switch can be optically connected to any of the optical fibers on another side of the switch. If all of the optical paths within the switch are in the same plane and at the same time all actuators within the switch can only be in either ON or OFF position, the cross-connect switch is referred to as being 2-dimensional. For example, a 2-dimensional optical cross-connect switch can be implemented with a planar array of mirrors for switching light, as described above, between optical fibers. For such an implementation to be usable, all the mirrors within the switching mirror array must be able to remain parallel to each other in order to permit individual alignment of collimating lenses for the optical fibers connected to the switch. At the same time it is preferable for the switch to have uniformity of optical insertion loss that varies less than 1 decibel (dB). Additionally, the switch should have low optical insertion loss and yet be economical to manufacture. Furthermore the switch may be subject to various industry standards such as Telcordia GR-1221, Generic Reliability Assurance Requirements for Passive Optical Components, and GR-1073, Generic Requirements for Fiber Optic Switches, both published by Bellcore, Bell Communications Research.
U.S. Pat. No. 5,841,917 issued to Jungerman et al. discloses an optical cross-connect switch incorporating a pin grid actuator to selectively position mirrors relative to light beams in the switch. Due to the inherent rotatability of the pins, it is difficult to provide precise parallel alignment of the mirrors. Furthermore, the vertical translation movement of the pins used for positioning and repositioning the mirrors provides poor repeatability for parallel alignment of the mirrors due also to the inherent rotatability of the pins.
As can be seen, there is a need for an optical cross-connect switch in which the mirrors can be precisely aligned and which has excellent repeatability for precise repositioning of the mirrors. Also, there is a need for an optical cross-connect switch with excellent repeatability for parallel alignment of the mirrors that meets industry standards such as Telcordia GR-1221 and GR-1073.